For many years, it has been recognized that the use of fixed or pop-up spray heads is the preferred type of irrigation system for use in situations where the available water supply pressure is relatively low or the area to be irrigated is relatively small and irregular in shape. One reason for this is that spray heads, which are relatively inexpensive to manufacture and maintain, and are available in a variety of full and part-circle configurations, operate on water supply pressures typically ranging between about 15 and 30 psi, and produce fan-shaped sprays which extend radially outwardly from the spray head over distances between about five and twenty feet, depending upon outlet nozzle size and water pressure. Further, in more recent years, spray heads have been developed to have matched precipitation rates so that the rate of water application produced by a given size full circle spray head is the same as that for the same size part circle spray head operating at the same supply pressure. That is, the spray heads are designed to discharge proportional gallonages of water that match the arc or part of a circle they cover so that, for example, a full circle spray head discharges twice the gallonage per unit time than that discharged by a half-circle spray head, and a quarter-circle spray head discharges half that of a half-circle spray head.
Matched precipitation rate spray heads are available in both metal, usually brass, and plastic, usually molded high strength material such as ABS plastic, and normally are coupled to the outlet of a stationary or pop-up tubular riser. Pressurized water admitted to the riser is projected outwardly by the spray head nozzle outlet as a pressurized fan-shaped spray which extends radially outwardly and upwardly away from the spray head. Ideally, the water fall-out distribution pattern produced by a spray head, like substantially any irrigation sprinkler, should be a straight line, 30 degree sloped wedge with the maximum precipitation at the spray head and zero at the maximum radius of water throw. With the ideal distribution pattern, the spacing between adjacent spray heads in a system should be equal to the maximum radial distance of throw so that the resultant precipitation rate over the area between sprinklers is uniform.
While the use of both metal and plastic spray heads have met with wide acceptance, one problem that has long plagued such spray heads is the inability of the spray head to disburse water in the immediate area around the spray head itself. That is, spray heads have typically produced distribution patterns which have maximum fall-out commencing approximately two feet radially away from the sprinkler, and thereafter reducing to zero at the maximum distance of throw. Thus, the fall-out distribution pattern of water from both metal and plastic spray heads has generally resulted in little or no appreciable water in the area extending from the spray head radially outwardly to about two feet away, thereby producing an arcuate "dead zone" extending outwardly approximately two feet.
To compensate for this problem, it is common practice in the industry to install the spray heads of a sprinkler system two feet closer together than should be required. While closer spacing does help alleviate the problem in the absence of wind, the closer spacing of spray heads results in an increase in the number of spray heads required for a given area, thereby increasing the cost of both material and labor, and total water consumption.
While attempts have been made to solve the problem of a lack of close-in water from spray head type sprinklers, none has proved commercially successful. One attempt to resolve this problem in part-circle metal spray heads has been the addition of a machined arcuate slit in the body of the spray head below the nozzle outlet and which permits a small portion of the supply water to be disbursed as a low volume, high pressure fan-shaped spray below the main spray. Although the addition of such a machined slit has improved the water distribution pattern between three and six feet radially outwardly of the spray head, has been found to have little effect on the area between zero and two feet, that area still receiving essentially no water fall-out. One reason that the use of an additional machined slit is believed to have been unsuccessful in solving this problem is that the slit must be so small in size that it becomes readily and quickly clogged by particles in the water, thereby becoming inoperative.
Thus, there exists a need for a spray head type sprinkler having the ability to disburse water to the immediate arcuate area between zero and two feet radially outwardly of the spray head so as to more closely approximate the ideal distribution pattern, yet which is simple in design, low in cost of manufacture and assembly, and reliable in use to achieve matched precipitation rates. As will become apparent hereinafter, the present invention satisfies this need in a novel and nonobvious manner.